The invention relates to a novel process for the production of citric acid from 3-methylene-1,5-pentanediol, and also to a novel process for production of citramalic acid from 3-methyl-3-buten-1-ol.
In addition to the substantial use of citric acid in soft drinks and other foods, sodium citrate appears to be an excellent replacement for the phosphate builders of the detergent art and various other uses for citric acid have been developing. However, the principal source for citric acid is from the fermentation of organic material such as molasses. Such a process is not completely satisfactory, especially where increasingly large amounts of citric acids are required.
Citric acid is a complex molecule having the following structure: ##STR1## No commercial routes have been developed to date for the synthesis of the complex citric acid molecule. As pointed out in Chemical Week, April 10, 1974, at page 29, entitled "New Uses May Make Citric's Cup Run Over":
"Synthetic routes to citric also have been explored, but no commercially usable process have been devised. The citric molecule is extremely complex, requires too many steps for economic synthesis." PA1 "It has been found that, although ethylene and olefins [other than C.sub.3 or C.sub.4 olefins] such as octylenes and cyclohexene may be suitably nitrated in the absence of solvent, i.e., by addition to liquid tetroxide, yet propylene and the butylenes give rise to partly oxidised substances containing little or no dinitroparaffin unless an ether- or ester-type solvent is used."
However, the present invention disclosed herein provides a process for making citric acid relatively inexpensively, and with few steps and commercially available feed.
The present invention concerns synthesis of citric acid from a feed material containing both olefin unsaturation and hydroxyl groups and using nitrogen dioxide and nitric acid. As used herein the term nitrogen dioxide includes its equivalent equilibrium form dinitrogen tetroxide. Art concerning olefin reactions with nitrogen dioxide and nitric acid teaches that the typical products of the reaction are nitro paraffins and nitro alcohols. Propylene and isobutene have been indicated to be exceptions to this general rule in that propylene can be oxidized with nitrogen dioxide and nitric acid to hydroxy acid, namely hydroxy propionic acid (lactic acid); and isobutene can be oxidized to alpha-hydroxy isobutyric acid. Thus, the work as reported by Levy and Scaife, J. Chem. Soc., London (1946), 1093, indicated that typically with higher olefins, that is olefins above isobutene, the normal reaction product with nitrogen dioxide and nitric acid is a dinitro paraffin. Levy and Scaife pointed out at page 1094:
Other pertinent art concerning reaction of olefins with nitrogen dioxide and/or nitric acid include: Muller et al. U.S. Pat. No. 3,324,168; a Russian article by B. F. Ustavshchikov et al., Doklady Akademii Nauk, S.S.S.R., Vol. 157, pp. 143-146, July 1964, entitled "On the Course of the Reaction of the Simplest Olefins with Liquid Nitrogen Tetroxide"; Gardner et al U.S. Pat. No. 2,847,453; Robertson et al. U.S. Pat. No. 2,847,465; and the brochure "Nitrogen Tetroxide" by Hercules, Incorporated, 1968.
Belgian Patent 775,729 to Washecheck discloses the oxidation of n-alkanol to a carboxylic acid using nitric acid. According to the Washecheck reference the saturated alcohols are advantageously oxidized with nitric acid using a vanadium catalyst.
The prior art does not appear to disclose treatment of any C.sub.6 or similar unsaturated alcohol with nitrogen dioxide and nitric acid to obtain a polybasic hydroxy acid. Also the prior art discloses only complex routes for the synthesis of citric acid, see, for example, U.S. Pat. Nos. 3,356,721; 3,852,322; and 3,843,692.
According to another embodiment of the present invention citramalic acid is produced. Citramalic acid occurs naturally in many foods, e.g., apples, pears, bananas, etc. Synthetic citramalic acid has been made by condensation of hydrogen cyanide with ethyl acetoacetate, but this process is too expensive for commercial use. Citramalic acid is useful as an acidulant for soft drinks and the like. It is also useful in the production of citraconic acid and itaconic acid.